| The traditional high-gain antennas for long-distance communications include reflector antennas and antenna arrays. The former have higher radiation efficiency but usually occupy a large volume. The latter on the other hand are planar and compact but have a complicated feeding network which lowers the efficiency. The bandwidth is also a limitation. Planar microstrip reflectarray antennas combine the advantages of them, such as lower mass and volume, ease of manufacture, with possibilities of beam shaping and electronic beam control although the bandwidth is still a limitation.However rapid developments in several aspects are overcoming most limitations.This dissertation mainly concerns the multi-polarization reflectarrays. A novel reflectarray has been successfully proposed, designed, manufactured and tested. With a linearly-polarized(LP) feeder, the antenna can transform the LP incident wave into a circularly-polarized(CP) one. Both LHCP and RHCP waves can be obtained by rotating the LP feeder from the polarization angle 45° and 135°. In addition, LP radiation can also be obtained, including horizontal-polarized and vertical-polarized wave, when the polarization angle of the feeder is 0° or 90°. In this dissertation, it is the first time to systematically address this polarization reconfigurable performance in reflectarrays and demonstrate it in simulations and experiments.The reflectarray consists of two double-layer dipoles orthogonally printed on the two sides of a dielectric substrate. It was demonstrated that the mutual effect between the two adjacent orthogonal dipoles is minor, making it possible to independently design the phase compensation for the two orthogonal polarizations along the two dipoles. With a LP feeder, multi-polarization waves, such as horizontal-polarized,vertical-polarized, LHCP and RHCP waves, can be obtained by the proposed reflectarray, depending on the polarization angle of the LP feeder. In addition, all the different polarized waves can also be obtained by rotating the reflectarray while fixing the feeder. Simulations and measurements validate the performance.Experimental results show 3-dB axial-ratio bandwidths of 16.3% and 16.8% and 3-dB gain bandwidths of 14.1% and 11.6% for LP-LHCP and LP-RHCP cases respectively.Reasonable LP-LP results were also obtained. Based on these results, the proposed reflectarray is suitable for multi-polarization applications requiring LPCP/RHCP and/or horizontal/vertical-LP.Secondly, a method to broaden the gain bandwidth of the printed microwave Fresnel zones plate reflector antennas was demonstrated based on the double-layer-dipole element proposed above. By decreasing the size of the double-layer-dipole element, for example, from λ/4 × λ/4 to λ/8 × λ/4, the gain bandwidth of the Fresnel zones plate reflector antenna can be improved. A novel Fresnel zones plate reflector antenna was designed at K band. Measurements of the prototype show that a 3-dB gain bandwidth of 24.9% with a peak gain of 32.1 dBi and a peak aperture efficiency of 58.6% was achieved. The proposed technology could be used in radar, satellite communication systems and other wideband high-gain applications. |
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